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Oct. 13, 2010 -- The idiom “a dog’s life” suggests that pooches have it made when it comes to happiness, but new research indicates that the emotional states of dogs can be as varied as the moods of their owners.

Dogs can see their food bowls as half empty rather than half full, just as human pessimists see a glass of water as half empty instead of half full.

British researchers who tested separation reactions of dogs say they found that some dogs are more likely than others to become depressed and anxious when left alone, causing them to bark, scratch at doors, chew on furniture, and generally misbehave.

On the other hand, optimistic dogs are more likely to behave better and become more relaxed when left alone.

Mike Mendl, PhD, head of animal welfare and behavioral research at the University of Bristol, and colleagues, studied 24 dogs, males and females, that had been sent to two animal centers.

Each dog was tested beforehand for separation anxiety-related behaviors. A researcher played with each dog in an isolated room for 20 minutes.

The next day the dogs were taken back to their rooms and left alone for five minutes while video cameras recorded their behavior.

Some of the dogs barked, jumped on furniture, and scratched at the door, but the “optimistic” ones did not -- or didn’t do it as much.

To study optimistic or pessimistic tendencies, the dogs were trained so that when a bowl was placed at one location in a room, it contained food, but when put somewhere else, it didn’t. Then the bowls were placed at ambiguous locations between the positive and negative positions.

“Dogs that ran fast to these ambiguous locations as if expecting the positive food reward were classed as making relatively ‘optimistic’ decisions,” Mendl says in a news release. "Interestingly, these dogs tended to be the ones who also showed least anxiety-like behavior when left alone for a short time.”

Separation Anxiety

He says about half of dogs may at some point engage in behaviors related to separation anxiety, such as barking, scratching, or tearing things up when separated from owners.

“Our study suggests that dogs showing these types of behavior also appear to make more pessimistic judgments generally,” he says.

“We all have a tendency to think that our pets and other animals experience emotions similar to our own, but we have no way of knowing directly because emotions are essentially private,” he says. “However, we can use findings from human psychology research to develop new ways of measuring animal emotion.”

It’s known that the emotional states of people affect their judgments, and that happy people are more likely to judge an ambiguous situation in a positive way. And it’s apparently the same with dogs.

“What our study has shown is that this applies similarly to dogs -- that a ‘glass-half-full’ dog is less likely to be anxious when left alone than one with a more pessimistic nature,” Mendl says.

Negative Behaviors

The study shows that dogs that exhibit negative behaviors, such as barking or engaging in “toileting” problems, appear to make more pessimistic judgments in general.

The study is published in the Oct. 12 issue of the journal Current Biology.

Samantha Gaines, DVM, deputy head of the Companion Animals Department at the Royal Society for the Prevention of Cruelty to Animals, says many dogs are abandoned because they exhibit separation-related behaviors.

The new study “suggests that at least some of these dogs may have underlying negative emotional states, and owners are encouraged to seek treatment to enhance the welfare of their dogs and minimize the need to relinquish their pet,” she says in the news release. “Some dogs may also be more prone to develop these behaviors and should be re-homed with appropriate owners.”

The research raises the possibility that some dogs may be more prone by nature to responding anxiously when left alone than others, and that this is related to their general mood.

That’s an important finding, because separation anxiety is common in dogs, and knowing which ones are or aren’t pessimists “is very important for ensuring good dog welfare,” Mendl says.

“Some owners think that dogs showing anxious behaviors in response to separation are fine and do not seek treatment for their pets.”